The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a carrier head for a chemical mechanical polishing apparatus.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, it is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly non-planar. This non-planar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a xe2x80x9cstandardxe2x80x9d or a fixed-abrasive pad. A standard polishing pad has durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles, if a standard pad is used, is supplied to the surface of the polishing pad.
The effectiveness of a CMP process may be measured by its polishing rate, and by the resulting finish (absence of small-scale roughness) and flatness (absence of large-scale topography) of the substrate surface. The polishing rate, finish and flatness are determined by the pad and slurry combination, the relative speed between the substrate and pad, and the force pressing the substrate against the pad.
A reoccurring problem in CMP is the so-called xe2x80x9cedge-effectxe2x80x9d, i.e., the tendency of the edge of the substrate to be polished at a different rate than the center of the substrate. The edge effect typically results in over-polishing (the removal of too much material from the substrate) at the substrate perimeter, e.g., the outermost five to ten millimeters of a 200 mm wafer. Over-polishing reduces the overall flatness of the substrate, causing the edge of the substrate to be unsuitable for integrated circuit fabrication and decreasing the process yield.
In one aspect, the invention is directed to a carrier head for a chemical mechanical polishing apparatus. The carrier head has a carrier base, a retaining ring, a flexible membrane, and a shim. The retaining ring includes a lower portion having a bottom surface for contacting a polishing pad during polishing and made of a first material, and an upper portion made of a second material which is more rigid than the first material. The flexible membrane has a central portion that provides a substrate mounting surface and an outer portion located between the base and the upper portion of the retaining ring. The shim is located between the carrier base and the upper portion of the retaining ring.
Implementations of the invention may include one or more of the following features. A second passage in the retaining ring may align with a first passage in the carrier head. A bolt or screw may extend through the first and second passages to secure the retaining ring to the carrier base. The bolt or screw may extend through an aperture in the shim into the second passage in the retaining ring. The second passage may not extend into the lower portion of the retaining ring. The shim may be composed of stainless steel. The first material may be tube PPS and the second material may be stainless steel. A seal may be clamped between the outer portion of the flexible membrane and the upper portion of the retaining ring to seal a chamber between the carrier base and the flexible membrane.
In another aspect, the invention is directed to a retaining ring for a carrier head having a mounting surface for a substrate. The retaining ring has a generally annular lower portion having a bottom surface for contacting a polishing pad during polishing and made of a first material which is inert in a chemical mechanical polishing process, and a generally annular upper portion joined to the lower portion and made of a second material which is more rigid than the first material. The first material is tube PPS and the second material is a metal.
In another aspect, the invention is directed to a retaining ring for a carrier head having a mounting surface for a substrate. The retaining ring has generally annular lower portion and a generally annular upper portion joined to the lower portion. The lower portion has a bottom surface for contacting a polishing pad during polishing and a plurality of channels in the lower surface of the retaining ring to carry slurry inwardly. The channels have a depth of at least about 0.14 inches. The lower portion is made of a first material which is inert in a chemical mechanical polishing process. The upper portion is made of a second material which is more rigid than the first material.
In another aspect, the invention is directed to a method of using a retaining ring. In the method, the retaining ring is secured to a base in a carrier head, and an outer edge of a flexible membrane is clamped between the retaining ring and the base. A first plurality of substrates are polished with the carrier head with a lower surface of the retaining ring contacting a polishing surface. The retaining ring is removed from the carrier head after the lower surface of the ring has been worn by a first amount. The retaining ring is resecured to the carrier head with a first shim between the base and the retaining ring, and a second plurality of substrates are polished with the carrier head.
Implementations of the invention may include one or more of the following features. A first seal may be secured between the flexible membrane and the retaining ring before polishing the second plurality of substrates. The retaining ring and first shim may be removed from the carrier head after the lower surface of the retaining ring has been worn by a second amount, the retaining ring may be resecured to the carrier head with a second shim between the base and the retaining ring, and a third plurality of substrates may be polished with the carrier head. A second seal may be secured between the flexible membrane and the retaining ring before polishing the third plurality of substrates.
In another aspect, the invention is directed to a kit with a retaining ring with an upper portion, a shim to be inserted between a base of a carrier head and the upper portion of the retaining ring, and an annular seal to be inserted between a flexible membrane and the retaining ring. The retaining ring includes a lower portion having a bottom surface for contacting a polishing pad during polishing and made of a first material, and an upper portion made of a second material which is more rigid than the first material. A plurality of channels are formed in the bottom surface of the retaining ring for carrying slurry inwardly.
In one aspect, the invention is directed to a carrier head for a chemical mechanical polishing apparatus. The carrier head has a substrate mounting surface and a retaining ring to maintain a substrate beneath the mounting surface during polishing. The retaining ring includes a lower portion having a bottom surface for contacting a polishing pad during polishing and made of a first material, and an upper portion made of a second material which is more rigid than the first material.
Advantages of implementations of the invention may include zero or more of the following. The edge effect may be reduced, and the resulting flatness and finish of the substrate may be improved. The retaining ring may have an improved lifetime.
Other advantages and features of the invention will be apparent from the following description, including the drawings and claims.